<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
     .big{
        display: flex;
        justify-content: center;
        align-items: center; 
     }
     .box{
        width: 200px;
        height: 200px;
        border: 1px solid red;   
     }   
    </style>
</head>
<body>
 <div class="big">
    <div class="box">
        这是内容
    </div>
 </div>
   


    <script>
   //  let arr = [1, 5, 3, 4, 1, 3 ,2 ]
   //  let myset = new Set()
   //  arr.forEach( item => myset.add(item))
   //  // set -- array
   //  let ok = [...myset]
   //  console.log( ok  );

    let n  = 3.1415;
    console.log( Math.ceil(n) );
    console.log( Math.floor(n) );
    console.log(  n.toFixed(2) );

    // 数据库24条， 每页10条   一共 24/10=3 页

    </script>
</body>
</html>